In oocytes, the translation of many dormant mRNAs is regulated by the length of the poly (A) tail. The poly (A) status is controlled by a conserved sequence present in the 3' untranslated region (UTR), designated the adenylation control element (ACE). We will exploit this regulatory scheme to study the control of mouse oogenesis and early development as follows: 1. Using the ACE sequence, we will selectively clone a set of mRNAs whose expression is under poly (A)-dependent translational control. Using a variety of approaches, we will systematically address the significance and function of these mRNAs in early mouse development. 2. We will perform a mutagenic analysis of the ACE element and surrounding sequences to investigate the exact requirements for both shortening and elongation of the poly (A) tail. These experiments may shed light on the mechanism by which different dormant mRNAs are activated for translation at various times in development. 3. We will investigate the molecular aspects of cytoplasmic regulation of poly (A) tail length in mouse oocytes. Using probes directed against molecules that participate in nuclear polyadenylation from other species, we will attempt to identify the mouse oocyte factors which interact with the cytoplasmic dormant mRNAs and control their poly (A) status. These factors could then be used to isolate other novel components of the system.